Tourette's Syndrome (TS) is an idiopathic hyperkinetic movement disorder marked by the presence of tics and psychiatric manifestations. Clinical and pathological data implicate alterations of striatal function in the pathophysiology of TS. The inadequacy of existing animal models, however, has resulted in incomplete knowledge of the mechanisms underlying the pathophysiology of tics and better understanding of the pathophysiology of tics is necessary to develop improved symptomatic therapies for tics. Clinical pharmacology and other data suggest that abnormalities of striatal dopaminergic neurotransmission are involved in the pathophysiology of hyperkinetic tics. Positron emission tomography with appropriate ligands offers the opportunity to probe striatal dopaminergic function in TS. We propose to probe striatal dopaminergic function in patients with TS by using [11C]dihydrotetrabenzine (DTBZ) as a measure of striatal dopamine terminal integrity.